Certain phorbol esters, polar solvents and retinoids have been identified as in vitro inducers of human myeloid leukemic cell differentiation. However, the mechanisms by which these diverse classes of agents induce differentiation remain ulcer. Furthermore, it is not clear whether most agents that induce differentiation in vitro exert similar effects in vivo. The proposed studies will address these two related issues. Few insights are presently available regarding the intracellular signaling events activated by inducers of leukemic cell differentiation. However, recent studies have demonstrated that different classes of inducers similarly activate expression of the c-jun and EGR-1 early response genes. The proposed studies will focus on the signaling mechanisms responsible for the induction of myeloid differentiation. The proposed studies will also continue to examine the therapeutic effects of differentiating agents in the treatment of myelodysplastic syndromes and acute myeloid leukemia. The induction of differentiation in vivo will be assessed by monitoring clonality of leukemic blasts and mature blood cells. The specific aims are: 1) to determine the involvement of early response genes in signaling events associated with the induction of monocytic differentiation; 2) to further define the role of protein kinase C activity in the differentiation of myeloid leukemia cells; 3) to utilize insertional mutagenesis for the identification of genes involved in the differentiation of myeloid leukemia cells; and 4) to further study the effects of differentiating agents in the therapy of myelodysplastic syndromes and acute myeloid leukemia.